The structure and mechanism of action of the (Na ion plus K ion)-ATPase and the Ca 2 ion-ATPase (from sheep kidney and rabbit SR, respectively) will be investigated using nuclear magnetic resonance (NMR) and electron spin resonance (ESR) spectroscopy, kinetic studies and fluorescence measurements. This work is directed toward a characterization of metal ion and substrate binding sites using suitable paramagnetic probes and ion or substrate analogs. Suitable analysis of dipolar relaxation between the paramagnetic probes and the observed nuclei of ion or substrate analogs can, under suitable conditions, be used to obtain structural and kinetic information about these transport enzymes.